Organic Chemistry - Organic Crackers -II

39

Pritish Chakraborty ·2010-02-24 11:56:32

1)
Bromobenzene -----(Dow's process)--> Phenol.
Phenol + Cl₂/FeCl₃ ---> para-chlorophenol
Para-chlorophenol ---(Dow's process)--> 4-hydroxyphenol
4-hydroxyphenol + Sodium/Sodium chloride --> 4-methoxyphenol

2)
Nitrobenzene + conc HNO₃/conc H₂SO₄ --->
Dinitrobenzene (meta position)

Dinitrobenzene + (NH₄)₂S ----> m-nitro aniline

m-nitroaniline + NaNO₂/HCl ---> Diazonium salt

Diazonium salt + H₂O/warm ---> m-nitrophenol

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13

Avik ·2010-02-24 12:04:26

1) Dow's process gives low yield naa & takes place in drastic conditions ? Isn't there a better alternative to insert -OH in the ring (frm a halide, apart frm the diazonium one) ?

2) [1] Bahut sahi!

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39

Pritish Chakraborty ·2010-02-24 23:07:48

There are 5 methods to prepare a phenol....Cumene-hydroperoxide method, Dow's process, Diazonium salt method, from benzene sulphonates, and from salicylic acids. The one involving a halide directly attached to benzene ring is Dow's process..you may say yield is low because it follows benzyne mechanism. The other way to kick a halide out is the S_NAr pathway, involving electron withdrawing groups...here you go.

Chlorobenzene + Cl₂/FeCl₃ ---> para-dichlorobenzene

Para-dichlorobenzene + conc HNO₃ ---> Nitration at ortho positions.

1,4-dichloro-2,6-dinitrobenzene + sodium methoxide(1 mol) ---> 4-methoxy-2,6-dinitro-chlorobenzene (since NO₂ groups make benzene acidic, it easily undergoes the nucleophilic substitution reaction)

4-methoxy-2,6-dinitro-chlorobenzene + conc NaOH(1 mol) ---> 4-methoxy-2,6-dinitrophenol (Again S_NAr)

4-methoxy-2,6-dinitrophenol + Sn/HCl + NaNO₂/HCl + H₃PO₂ ---> 4-methoxyphenol (Diazonium salt formation and reduction)